Is there a single character day of the week convention?

Question

Is there a single character convention for the days of the week in English (or programmer-specific) and if so what is it? I realize this could be an English language question but I think it has special significance for programmers.

Maybe something like:

Monday    Mon  MO  M
Tuesday   Tue  TU  T
Wednesday Wed  WE  W
Thursday  Thu  TH  U
Friday    Fri  FR  F
Saturday  Sat  SA  S
Sunday    Sun  SU  N

Answer 1

Understood that this question is an old one, but for new searchers (like me) who bump into it: The MTWRFSU convention for unambiguous single-letter references to Monday through Sunday appears to be relatively common. I first encountered it at George Washington University in the late 80s, where it was used in the class registration process. Googling "mtwrfsu" shows that it persists in academic IT all over the US, for example: https://sa.ucla.edu/ro/Public/SOC/Results/ClassDetail?term_cd=161&subj_area_cd=WL%20ARTS&crs_catlg_no=0174A%20%20%20&class_id=401744210&class_no=%20002%20%20

FWIW, I've been using it regularly in schedule annotation in English-language business contexts for 30+ years and have very rarely seen anyone not get it, without any explanation required.

Answer 2

Perhaps this is an authority? They recommend, M T W R F S U http://eventguide.com/topics/one_digit_day_abbreviations.html

In any case, what's probably most important is that the end-user has documentation telling which arbitrary choice you've decided on.